POWER 113 the bountiful stores on which man now draws with care- less and prodigal ease. Ships that burn oil must have it come to them from sources outside Great Britain. Well, then, can we expect ships to return to the use of coal as fuel ? For some classes of ships I think we may, though not all classes. Neither in the Navy nor in what one may call the upper division of the Mercantile Marine—the luxurious express liners which carry fastidious passengers and must keep to a time-table that means quick fuelling —can one expect a reversion to coal so long as oil fuel can be got at anything like its present price. But with cargo liners and big cargo boats, the case is different. They do offer a possible field for the use of coal, a field where I believe its use would be economically sound as well as of great national advantage. In the running of such ships, the incidental conveniences of oil fuel count for less. The cost of fuel is a relatively big factor, and there is a clear advantage in being able to burn either coal or oil at option, according to the local cheapness of supply. There the geared turbine with coal fuel can more than hold its own provided the steam plant em- bodies the conditions that make for high efficiency, con- ditions which are now known to be attainable in marine practice. I think those engineers are right who contend that for such ships a highly economic mode of working would be to use pulverized coal for steam-raising in a small number of large boilers of the water-tube type, with a pressure of, say, 500 Ib. and a temperature of 750° F., each boiler having its own pulverizing mill and being fitted also for burning oil as an alternative fuel. In such a scheme there would be no untried elements, but the combination of the elements would be experi- mental, and a conclusive demonstration of its advantages can be obtained only by testing it out on a large scale in sea-going ships, trading on more than one route. An H